The activities of glucokinase, glucose-6-phosphatase, phosphofructokinase, fructose-1,6-diphosphatase, pyruvate kinase and phospho-enol-pyruvate carboxykinase in rat livers perfused in the absence and presence of glucagon will be examined. Also the kinetic properties of fructose-1,6-diphosphatase in rat livers perfused in the presence and absence of glucagon will be investigated. The objectives of this investigation are to determine if a number of gluconeogenic and glycolytic enzymes in the rat liver are subject to phosphorylation and dephosphorylation as a result of the hormone treatment and to determine if this regulation is related to the stimulation of gluconeogenesis by glucagon. The results of these investigations will have direct biomedical relevance to the biochemical disorders accompanying metabolic diseases such as diabetes mellitus and hypoglycemia.